1. Field of the Invention
The present invention relates to an information processing apparatus, and more particularly, to an information processing apparatus in which a plurality of image files are simultaneously exchanged between a primary memory unit and a secondary memory unit at an optimum efficiency.
2. Description of the Related Art
A digital copier having an image memory unit therein enables a user to manipulate and edit documents while the documents are stored in the image memory unit. Among many functions realized by using the image memory unit, a function called “electronic sorting”, for example, uses the image memory unit to electronically sort the documents stored in the image memory unit and free the user from manually sorting. A digital copier having the electronic sorting function scans a plurality of pages, stores an image file of them in the image memory unit thereof, and prints a desired number of sorted copies by repeatedly printing a copy for the desired times. The digital copier having the electronic sorting function, however, requires a considerable memory capacity to store the image file, which causes a cost problem.
The following solutions to solve the cost problem are currently available:
1. using semiconductor memory devices as a primary memory unit and a low-cost storage media device such as a hard disk drive as a secondary memory unit;
2. using semiconductor memory devices as both a primary memory unit and a secondary memory unit, wherein image files to be stored in the secondary memory unit are compressed to reduce the required memory capacity; and
3. in the case of a digital complex apparatus including therein an image scanner, a printer controller, a file server, and a facsimile controller, and so forth, sharing a common memory resource among them.
A memory controller having a direct memory access data transfer mode (hereinafter referred to as a DMA controller or a DMAC) is often used to exchange an image file with such an image memory unit. The DMA controller uses information for controlling a memory region, called a descriptor, and exchanges the image file using a specific region in the image memory. It is possible to divide a memory region in which an image file is to be stored into a plurality of small memory regions and transfer the image file to the memory region using a plurality of descriptors each corresponding to one of the small regions. It is also possible to reduce the required memory capacity by using the image memory unit as a ring buffer, for example.
Since the DMA controller can monitor the beginning and the completion of data transfer designated by each descriptor, and can stop and resume the data transfer even in the middle of the image memory region, for example, the DMA controller is capable of providing flexible timing control and is applicable to a variety of applications.
In the case where a secondary storage apparatus such as a hard disk drive of which bit cost is lower than that of a semiconductor memory is used as a storage memory, such a secondary storage apparatus usually cannot simultaneously perform a plurality of data transfers (a data writing operation or a data reading operation). The DMA controller can virtually realize simultaneous multiple data transfers by dividing a data transfer operation using descriptors for time-sharing.
However, if a time-sharing method is used, time required for data transfer is not reduced. In the case of an image forming apparatus such as a copier and a printer, the data transfer time substantially affects the productivity of the image forming apparatus. The time-sharing method may result in the degrading of productivity.
Accordingly, it is important to reduce time required for data transfer to a secondary memory, apparatus by first compressing the data to reduce the file size thereof and using a secondary memory apparatus having a higher data transfer speed.
Additionally, since the time-sharing method complicates memory control, the secondary memory apparatus is conventionally controlled by an image input/output unit during data transfer instead of using the time-sharing method.
By the way, in the case of a conventional secondary memory apparatus, the speed of data transfer between a semiconductor memory and the conventional secondary memory apparatus is lower than that of data transfer between the image input/output unit and the semiconductor memory. Even if the size of image data is reduced by compressing, the speed of data transfer between the semiconductor memory and the conventional secondary memory apparatus is substantially the same as the speed of data transfer between the image input/output unit and the semiconductor memory. Accordingly, even if the transfer timing of the data transfer (including data conversion processing such as data compression) to the semiconductor memory and the transfer timing of the data transfer to the secondary memory unit are controlled independently and optimally, the productivity of the image forming apparatus is not improved very much.
However, the data transfer speed of secondary memory apparatuses such as a hard disk drive and the data compression rate and processing speed of data compression units is now considerably improved, and a variety of image input/output units that can be connected to an image forming apparatus have become available. Under such a situation, it is difficult to achieve the utmost performance of a memory unit and a data compression unit and improve the productivity using the conventional method of memory control.